In recent years, personal computers have pervaded into people's domestic lives. Other types of digital information devices, such as digital television sets or digital versatile disc (DVD) recorders, are also becoming popular. Under such circumstances, many people are constructing home networks including the aforementioned information devices as their principal components. Meanwhile, refrigerators, microwave ovens and other home appliances that are generally called “white goods” have now advanced features, and efforts are being made to also integrate these appliances into the home network. However, there are various kinds of practical problems to be solved in bringing the home network into popular use. One of the urgent tasks is to provide a user-friendly mechanism for operating the system. Accordingly, it is necessary to develop an easy-to-use user interface.
Nowadays, mobile phones are remarkably spreading their application areas. Many phone models come with digital cameras, some of which also have storage media. Recently, these mobile phones are used as information terminals in various application systems. In such a technical situation, the present inventors and others have proposed a remote control system using a mobile phone having a digital camera, as disclosed in Non-Patent Document 1. This system, called the “OPTO-NAVI” system, uses a mobile phone to create a user interface on which users can visually check various kinds of remote information devices and operate those devices on the screen.
In the OPTO-NAVI system, each information device to be controlled has a light-emitting diode (LED), through which the device transmits optical signals containing identification (ID) information specific to the device and other related information. The mobile phone receives the optical signals through its light-receiving module and recognizes the position of the information device concerned. Then, it displays an image of the surrounding space captured with its digital camera and indicates the position of each remote-controllable information device on the screen. Thus constructed, the OPTO-NAVI system provides an easy-to-use interface for users to operate various devices and appliances included in the home network.
Any information terminal (e.g. mobile phones) compatible with the OPTO-NAVI system has a dedicated image sensor for receiving the optical signals. The present inventors and others proposed such an image sensor in WO 2006/048987 A1, Non-Patent Document 2 and other documents. This sensor is a complementary metal-oxide-silicon (CMOS) image sensor intended to be installed in a mobile phone or other small-size, light-weight information terminals and used to take pictures in normal modes and also receive the aforementioned optical signals and read out the ID information from the signals with minimal power consumption. To satisfy these requirements, the image sensor has the characteristic function of reading out signals from a small number of pixels included in a limited, smaller range of image at a higher frame rate (at least higher than a normal frame rate) as well as the ordinary function of reading out all the pixel signals at the normal frame rate.
More specifically, the CMOS image sensor described in Non-Patent Document 2 can capture up to seven pieces of “ID images” (i.e. small images including one or more pixels receiving the optical signals containing the ID information) of 5×5 pixels at a frame rate of 1.2 kfps (kilo-frames per second) while repeatedly reading out QVGA images (320×240 pixels) at a rate of 30 fps. In this process, the high-speed readout operation is performed only on a limited pixel range surrounding the spot where the optical signals containing the ID information is received. This reduction in the number of pixels speeds up the pixel readout operation and lowers the power consumption.
In addition to the reduction of power consumed by the image sensor, it is important for the OPTO-NAVI system or other similar systems to suppress the power consumed by the signal-processing circuits (including digital signal processors or microcomputers) that locates the aforementioned optical signal containing ID information (this signal is called the “ID light” hereinafter) on the captured image and that receives the ID light. To satisfy this requirement, it is necessary to minimize the amount of calculation performed to locate the targeted ID light on the captured image. Decreasing the amount of calculation will also shorten the time required for locating the reception point of the ID light and enable the information terminal to make quicker responses to operations by the user. There is no conventional technique proposed to reduce the amount of calculation performed for the aforementioned purpose and improve the efficiency of determining the reception point of the ID light on the captured image.
[Non-Patent Document 1] Keiichiro KAGAWA, et al., “Jouhou Kaden No Bijuaru Maruchi Rimokon: Hikari Nabigeishon No Teian (Optical navigation: a ubiquitous visual remote-control station for home information appliances)”, Proc. of Optics Japan 2004, November 2004, pp. 112, 113
[Non-Patent Document 2] Koji YAMAMOTO, et al. “‘OPTO-NAVI’ Shisutemu Ni Muketa 30 fps Tsuujou Gazou/1 kfps ID Gazou Douji Satsuzou Kanou Na CMOS Imeeji Sensa (A CMOS Image Sensor for Capturing Normal Images @ 30 fps and ID Images @ 1 kfps/ID, for the “Opto-Navi” System)”, ITE Technical Report, vol. 29, No. 24, March 2005, pp. 9-12
Taking into account the above-described problem, the present invention intends to provide an information-processing device or information-processing system including an information terminal to be operated by users for collecting predetermined pieces of information from remote information devices by free-space optical communication, where the power consumption of the information terminal is suppressed by minimizing the amount of calculation performed to collect the aforementioned information.